Michał Bultrowicz - TDD of Python microservices
[22 July 2016 / 2016-07-22]
[Bilbao, Euskadi, Spain]
A framework-agnostic approach to creating Python microservices with a
I'll show how to utilize Docker and Swagger to create service and
contract tests that run your service as an independent process, as if
it was running in production, giving you and your team a higher degree
of confidence when introducing changes.
A little bit of a broader microservice, TDD and work management
context will also be given.
These will be my ideas on how to help a microservice-based (HTTP)
project by integrating testing into the development process (TDD).
I'll approach the testing pyramid presented in Martin Fowler's
"Microservice Testing" as well as the test variants in "Building
Microservices" (O'Reilly) and I'll show a way of how they can be
translated to real-life Python.
The main focus will be on "service tests" (aka. out-of-process
component tests) and contract tests. They both can be run relatively
fast on a development machine and can give fast feedback to the
developer, preventing many kinds of problems.
Service tests run the whole application process without any internal
modifications, but have to present the service with a fake "outside
world". I'll show how to fake external HTTP services with Mountebank
(similar to WireMock). Instead of faking other systems (like
databases) we can quickly spin up the real deal as a Docker container
from within the tests.
Contract tests check if the contract (interface) of your service with
the outside world is kept, so no external services should be broken by
the changes you are introducing. It can also work the other way
around, proving that your collaborators are keeping their part of the
deal. In both cases, Swagger (a RESTful API description scheme) and a
few clever tricks can be used for significant advantage.